Target assembly for storage tubes and a method of making the same

ABSTRACT

A target assembly for storage tubes comprising a film of an organic compound of a resistivity of at least 1015 ohms-cm deposited on a 500- to 1500-mesh metal screen. The target assembly is prepared by depositing droplets of the organic compound on the screen, rotating it in a spinner to cause the droplets to drift sideways to fill out the interstices and heating the compound at 100* to 200*C for about 3 hours.

United States Patent Koike et al.

TARGET ASSEMBLY FOR STORAGE TUBES AND A METHOD OF MAKING THE SAME inventors: Yujiro Koike; Haruo Maeda;

Tsutomu Nishino; Akimitu Aoyama; Yuji Mogi, all of Kawasaki, Japan Matsushita Electric Industrial Company Limited, Osaka, Japan Filed: Mar. 16, 1973 Appl. No.: 341,898

Assignee:

Foreign Application Priority Data Mar. 17, 1972 Japan u 47-27766 US. Cl. 313/394 Int. Cl. H01] 1/53 Field Of Search 313/68 R, 394

[ 1 May 20, 1975 [56] References Cited UNITED STATES PATENTS 2,538,836 1/1951 Jensen 313/68 R 3.061486 l2/1962 Day 3l3/68 R 3.6I7.79l ll/l97l Franz etal 313/94 Primary Examiner-Ronald L. Wilbert Assistant Examiner-Richard A. Rosenberger [57] ABSTRACT 3 Claims, 4 Drawing Figures PATENIED HAYZOIQYS F lg.

mgr/4 rm 2 m m FA 11 1 Fig. 2

Fig. 3- HEAT TARGET ASSEMBLY FOR STORAGE TUBES AND A METHOD OF MAKING THE SAME This invention relates generally to a target assembly for use with charge storage tubes, and in particular to a method of producing a target assembly having an organic compound film.

Storage of picture signals for a predetermined period of time will find many uses in future telecommunication applications including displaying of a still picture, such as documents, on a video telephone system, monitoring pictures being transmitted or received on a facsimile and displaying of picture signals interleaved with signals of the conventional broadcast television or CATV systems. Storage tubes will meet these requirements and a number of types of storage tube are already known in the art. One prior art storage tube is provided with a target assembly which comprises a photoconductive layer, or a photocathode as it is usually called in the art, placed on one side thereof facing the scene to be imaged and an insulating layer on the other for storing charges developed as a result ofa light incident upon the photocathode, the charged information being read out by impingement of an electron beam. Another prior art storage tube employs a writing gun instead of a photocathode for charging electrons on the target and a reading gun for discharging the electron charges. Still another type uses a single electron gun to serve the dual purposes of writing and reading binary information.

A target assembly used for such applications is composed of a metal screen on which a layer of an inorganic compound such as calcium fluoride (CaF silicon dioxide (SiO or such a porous inorganic compound as potassium chloride (KCl) is deposited. Another prior art target assembly comprises a silicon substrate and a layer of silicon dioxide deposited thereon in the form of a mesh or dots.

The important requirements for a charge storage target are uniformities of charge contrast, power of reso lution, image gradation and writing and reading speeds over the entire surface of the target. To meet these requirements it is necessary to ensure uniformities of secondary emission characteristics, film thickness of the insulator compound and electrical resistance and ca pacitance of the insulator compound.

In prior art methods of fabricating a target assembly, a number of complicated processes are required, which include vacuum evaporation, oxidization and photoetching. Products have to be transported frequently from one location to another during these process steps, and it often happens that the products are exposed to the outer environment, and thus increasing the probability of introducing harmful foreign particles into the products and of contaminating the surface thereof with dust. The introduction of foreign particles often results in nonuniform secondary emission characteristic. In addition, it takes long to manufacture and thus results in a high production cost.

Accordingly, it is an object of the present invention to provide a target assembly using an organic compound as a storage element.

Another object of the present invention is to provide a simplified method of producing at a low cost target assemblies having a uniform storage time from one sample to another.

Still another object of the invention is to provide an improved storage target assembly having a long lifetime.

These and other objects and features of the present invention will be more clearly understood from the fol lowing description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an enlarged side view of a target assembly according to the present invention showing droplets of organic compound deposited on a metal screen;

FIG. 2 is an enlarged side view of the target assembly of FIG. 1 showing the organic compound spread out over the surface of the screen;

FIG. 3 is an enlarged side view of the target assembly of FIG. 2 in solid state after a firing process; and

FIG. 4 is an enlarged side view of a pair of the target assemblies of FIG. 3 connected in rear-to-rear relation with each other.

A first embodiment of the present invention is shown in FIG. 1 and comprises a target assembly generally indicated at reference numeral 10. The target assembly 10 comprises a meshed metal screen 11 formed. for example, of copper and having a thickness of about 3 mi crons. On the screen 11 droplets 12 of an organic compound such as polyimide enamel, known under Duponts Trade Name Polyimide Wire Enamel or polyamideimide enamel are deposited by means of spraying or painting or other known methods. The screen 11 is then placed in a spinner (not shown) and rotated at high speed to cause the droplets 12 of the organic compound to drift sideways by centrifugal force and drift downwardly into the interstices 13 by gravita tional force. Because of the viscosity of the compound material, the droplets are spread out over the entire surface of the screen as shown in FIG. 2. Under this condition surface irregularities possibly develop over the target surface. Next, the screen 11 is heated in air to a temperature in the range of about lOU to 200C and maintained there for about 3 hours. During the heating process, the solvent of the organic compound is evaporated causing a mechanical stress to develop within the compound. The stress acts in such a way as to eliminate the surface irregularities, thus providing an organic compound film 14 with a uniform thickness over the entire target surface.

FIG. 4 illustrates a second embodiment of the invention. A target assembly 20 comprises a pair of targets 10 prepared by the method as previously described. The targets 10 are connected in rear-to-rear relation to each other with the screen sides facing outside. The tar get assembly 15 may be useful for two-gun storage tubes in which one side of the assembly 15 serves as a target for the writing gun and the other side as a target for the reading gun.

In the arrangements described above, the charge storage time is determined by the resistance measured across the interstice 13. The resistance is in turn determined by the size of the interstice and the thickness of the resultant organic compound film 14. For example, a 500- to l500-mesh screen and a film thickness of from about 1 micron to 20 microns result in a charge storate time in the range of 3 to minutes.

The metal screen 11 may be formed of any metal of the type which is stable in vacuum such as copper, aluminium and silver, or may be constructed on a glass screen of such material as to permit deposition of metal or conductive material thereon and to permit provision of an optically flat surface. in addition, the screen 11 may be of a grid type comprising a plurality of parallel metal strips. If metal strips are used in the arrangement of the target assembly 15, targets are connected in such a way that the strips of one target side run normal to the direction of the strips of the other target.

A test revealed that the target assembly constructed according to the present invention had no performance deterioration after application for a period of six months of an impacting electron beam accelerated by a potential of 100 eV onto the surface of the assembly.

The foregoing description shows only preferred embodiments of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the embodiments shown and described are only illustrative,

not restrictive.

What is claimed is:

l. A target assembly for use with charge storage tubes. comprising a screen having interstices therein and a film of an organic compound of a resistivity of at least 10 ohm-cm deposited on said screen, wherein said organic compound is selected from the group consisting of polyimide and polyamideimide, and wherein said compound has a uniform thickness over the entire target surface, whereby said organic compound is capable of storing electrostatic charges for an extended period of time.

2. A target assembly as claimed in claim 1, wherein said organic film has a thickness of at most 20 microns.

3. A target assembly as claimed in claim 1, wherein said screen is a 500- to lSOO-mesh screen. 

1. A TARGET ASSEMBLY FOR USE WITH CHARGE STORAGE TUBES, COMPRISING A SCREEN HAVING INTERSTICES THEREIN AND A FILM OF AN DEPOSITED ON SAID SCREEN WHEREIN SAID ORGANIC COMPOUND IS SELECTED FROM THE GROUP CONSISTING OF POLYIMID AND POLYAMIDERIMIDE, AND WHEREIN SAID COMPOUND HAS A UNIFORM THICKNESS OVER THE ENTIRE TARGE SURFACE, WHEREBY SAID ORGANIC COMPOND IS CAPABE OF STORING ELECTROSTATIC CHARGES FOR AN EXTENDED PERIOD OF TIME.
 2. A target assembly as claimed in claim 1, wherein said organic film has a thickness of at most 20 microns.
 3. A target assembly as claimed in claim 1, wherein said screen is a 500- to 1500-mesh screen. 